The Collaborative International Dictionary of English v.0.48:

Pian \Pian\, n. [Pg. pian, epian, or. Sp. pian; from the native
   name in South America: cf. F. pian.] (Med.)
   The yaws. See Yaws.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Yaws \Yaws\, n. [African yaw a raspberry.] (Med.)
   A disease, occurring in the Antilles and in Africa,
   characterized by yellowish or reddish tumors, of a contagious
   character, which, in shape and appearance, often resemble
   currants, strawberries, or raspberries. There are several
   varieties of this disease, variously known as framboesia,
   pian, verrugas, and crab-yaws.
   [1913 Webster]